Conventionally, it is known that selective bromination of aromatic compounds having an electron-attracting group is very difficult. As techniques related to such a reaction, it is known, for example as a method for preparing dialkyl 5-bromoisophtalate a method comprising brominating dimethyl isophthalate with bromine at the presence of bromine trifluoride (BrF3) to give dimethyl 5-bromoisophtalate in a 55% yield (J. Org. Chem., 58, 239 (1993)). This method, however, uses bromine trifluoride that is expensive and intractable, and leads an aimed product in a low yield. Therefore, the above-mentioned method is not practical.
An object of the present invention is to provide a process for preparing bromoisophthalic acid compounds, in particular 5-bromoisophthalic acid compounds and 4,5-dibromoisophthalic acid compounds in a selective manner and a high yield, by the use of bromine that is inexpensive industrially.
As a result that the present inventors researched eagerly on processes for preparing bromoisophthalic acid compounds and 4,5-dibromoisophthalic acid compounds can be prepared in a particularly selective manner and a high yield by the use of bromine that is inexpensive industrially, and completed the process for preparing bromoisophthalic acid compounds of the present invention.